serial: uartps: Fix multiple line dereference

Trivial patch which fixes this checkpatch warning:
WARNING: Avoid multiple line dereference - prefer 'port->state->xmit.tail'
+				port->state->xmit.buf[port->state->xmit.
+				tail], port->membase + CDNS_UART_FIFO);

Fixes: c8dbdc84 ("serial: xuartps: Rewrite the interrupt handling logic")
Signed-off-by: NNava kishore Manne <nava.manne@xilinx.com>
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/xilinx_uartps.c

@@ -321,8 +321,8 @@ static void cdns_uart_handle_tx(void *dev_id)
 			 * register.
 			 */
 			writel(
-				port->state->xmit.buf[port->state->xmit.
-				tail], port->membase + CDNS_UART_FIFO);
+				port->state->xmit.buf[port->state->xmit.tail],
+					port->membase + CDNS_UART_FIFO);
 
 			port->icount.tx++;